1. Field of the Disclosed Embodiments
This disclosure relates to systems and methods for implementing a peak-to-average power ratio (PAPR) reduction technique or scheme that may be particularly applicable for devices operating an Orthogonal Frequency-Division Multiple Access (OFDMA) modulation technique, including a next generation cable gateway and/or next generation cable modem, and/or a cable gateway system-on-chip (SOC), based on the DOCSIS standard.
2. Related Art
Much of the work in advancing communication technologies in recent years, particularly emphasizing higher data rates and transmission speeds, has focused on advances in wireless technology transmission and reception. Corresponding advances in communication capabilities and capacities for cable gateways and cable modems, and the technologies housed in these components, remain important. Consider that, for individual structures such as individual residential homes that include dispersed wireless networks internal to and throughout the structure, the wireless modem or modems deployed throughout the structure are likely connected to coaxial cables as a data transmission medium for the data to get to the structure where it is then disseminated throughout the structure wirelessly. In this regard, the cable backbone, which often includes some combination of fiber and coaxial cables (hybrid fiber/coaxial cable systems), forms a significant and equally important part of an overall broadband network system. In the hybrid fiber/coaxial cable systems, fiber transmission cables form a significant portion of the cable backbone, but the connections to individual structures and to the wireless modems deployed within those structures are often made using coaxial cables.
The standard by which data transmission by cable is defined is the Data Over Cable Service Interface Specification or DOCSIS. DOCSIS is an international telecommunications standard that permits, among other technologies, the addition of high-speed data transfer to an existing cable television (CATV) system. DOCSIS is employed, for example, by many cable television operators to provide Internet access over existing hybrid fiber/coaxial cable systems and network infrastructures. DOCSIS, therefore, defines the mechanism by which data is transmitted over cable transmission lines to individual structures and the devices and access points that may be housed in those structures.
The DOCSIS 3.0 standard regarding physical layer specifications was released in its latest revision on Nov. 17, 2011 (the first revision was issued on Aug. 4, 2006). DOCSIS 3.0 is generally a specification revision that realized significantly increased transmissions speeds, and introduced support for Internet Protocol version 6 (IPv6). Current cable systems based on the DOCSIS standard use the physical layer defined in the International Telecommunication Union (ITU) Recommendation J.83 Annexes A, B or C. This standard is based on single-carrier quadrature amplitude modulation (QAM) and the physical layer channel bandwidths of 6, 7 or 8 MHz. Current versions of DOCSIS specify that 64-level or 256-level QAM (64-QAM or 256-QAM) be used for modulation of the downstream data transmissions, using an ITU-T J.83-AnnexB standard for 6 MHz channel operation, and a DVB-C modulation standard for 8 MHz channel (EuroDOCSIS) operation. QAM represents a format by which digital data is transmitted over coaxial cables. Current standardization activities are exploring the use of Orthogonal Frequency Division Multiplexing (OFDM) for the downstream carrier modules and OFDMA for the upstream with individual OFDM carriers modulated with 1024-level or 4096-level QAM.
A DOCSIS architecture includes two primary components: a cable modem (CM) located at the end-user structure, and a cable modem termination system (CMTS) located, for example at the CATV head end. Cable systems supporting on-demand programming use a hybrid fiber/coaxial cable system. Fiber optic lines bring digital signals to nodes in the system where they are converted into RF channels and modem signals on coaxial trunk lines. DOCSIS is exploring mechanisms to further increase bit rates carried by the coaxial cable trunk lines.
OFDMA is a multi-user version of the popular OFDM digital modulation scheme. Multiple access is achieved in OFDMA by assigning subsets of carriers (subcarriers) to individual users allowing simultaneous low data rate transmission from several users. OFDMA, therefore, provides a simple and robust scheme to avoid multipath interference. OFDMA can achieve a higher multiple-input/multiple-output (MIMO) spectral efficiency due to providing flatter frequency channels than, for example, in systems incorporating Code Division Multiple Access (CDMA). OFDMA allows simultaneous low-data-rate transmission from several users with lower maximum transmission powers for low data rate users.
OFDMA operates roughly as follows. Based on feedback information about channel conditions, adaptive user-to-subcarrier assignment is implemented. If this assignment is done sufficiently fast, this further improves the OFDM robustness to fast fading and narrow-band co-channel interference, and makes it possible to achieve better system spectral efficiency. Different numbers of subcarriers can be assigned to different users to support different Quality of Service (QoS) levels.
OFDMA is highly suitable for broadband wireless networks due to certain advantages including scalability, MIMO adaptability, and advantageous use of frequency selectivity.